The present invention relates to hydroponics, and more particularly to hydroponic nutrient circulation systems.
Hydroponics is the method of growing plants without soil, using a solution of water and dissolved mineral and/or organic nutrients. Only the roots are immersed in the nutrient solution, and sometimes only the tips of the roots are immersed. Because soil nutrients are not available to the plants, it is critical that all of the necessary nutrients be added and maintained in the correct ratios in the nutrient solution. Hydroponic nutrient solutions must be monitored to ensure that nutrient concentration, oxygen concentration, pH, and temperature are within desired ranges.
Hydroponic systems are widely used by hobbyists and commercial growers. Growers employ a number of techniques to provide access to nutrients and to maintain the proper nutrient mixture for the plants.
Hobbyists with limited production needs may use static systems in which the plants are supported above a tank of nutrient solution with only the roots extending into the solution. In these systems, to assure the roots are continuously immersed, water must be added to replace the water loss to transpiration and evaporation. The plants could die if the roots are out of the solution for only a few hours. Nutrient mixture ratios, pH, and temperature in each grow tank must be monitored and adjusted as nutrients are consumed by the plants and as nutrient concentration changes due to water level changes. Additionally, the plant roots must have access to oxygen. It is common practice to bubble air through the nutrient solution so that the solution absorbs sufficient oxygen to meet plant needs. Air pumps and air stones, the same as those used in aquariums, are used for this purpose.
It is common for commercial growers and hobbyists, looking for more efficient ways to grow larger crops, to use centralized reservoirs of nutrient solution delivered to multiple grow tanks using pumps. These types of systems are referred to as “recirculation systems.” They are more practical than static systems for growing large crops because nutrient solutions can be monitored and maintained in a single location rather than in each grow tank.
In one type of recirculation system, the solution from each growing tank is returned to the reservoir through gravity return pipelines. Automatic keep-full valves maintain reservoir level by adding water to the reservoir as the level drops. Proper nutrient mixture, pH, and temperature can be maintained for all of the grow tanks in the network by monitoring and adjusting the reservoir nutrient solution. The grow tanks still require aeration, which typically is provided by a large air pump feeding a distribution manifold so that air may be delivered to each grow tank. These systems require the grow tanks to be located above the level of the reservoir so that the gravity return lines can be used.
In another type of recirculation system, the multiple grow tanks and the reservoir all are at the same level. The grow pots are all connected to a common drain line so that they all have the same liquid level as in the nutrient reservoir. A pump in the reservoir delivers nutrient solution to each grow pot to provide a continuous supply of fresh nutrient. Air is supplied by way of an air pump with air stones in each grow tank. Drainpipe size is generally large to assure that a common level is maintained in all of the grow tanks and to assure that aggressive roots do not plug the drain ports in the grow tanks.
Systems that use multiple grow tanks connected at the bottom to a common reservoir at the same level as the grow tanks must all operate at the same liquid level as the reservoir and each other. This is not ideal if it is desired to adjust the level of an individual grow tank to accommodate different plants and root growth issues, or to use tiered benches to locate grow tanks at different elevations. The hydroponic method known as Deep Water Culture is often used in these systems. Plants sit above the nutrient solution with just some of the roots immersed in the solution. Grow tanks may have one or more plants. These systems are not suitable if roots require different nutrient levels or grow tanks are at different elevations.
Certain aspects of recirculation systems are less than ideal. The drain piping system must connect the reservoir directly with each grow tank. This requires leak-tight joints for grow tank gravity drain ports to connect with the drain line. Particularly in systems where grow tanks are elevated relative to the reservoir, this can be a complex, three-dimensional network of pipes and joints, thereby adding installation expense and making modifications problematic. Reconfiguring pipelines requires a shutdown of the operation, potentially leaving roots exposed to air. Reconfiguring pipelines also can take significant time, which adds to the risk of plant damage.
Aeration also presents problems. Aeration requires air pumps and lines, which adds cost. Air lines must be routed to all grow tanks adding to the network cost and complexity.
There are other problems related to the specific type of grow tank. The grow tanks that employ the hydroponic system known as Net Film Technique (NFT) use a thin film of liquid nutrient flowing from one end to the other in the bottom of a trough-type tank. This type of grow tank is widely used, for example, in commercial vegetable and herb operations. Many plants can grow side-by-side along the length of the trough. The plants sit in holes in the cover of the trough with the tips of their roots wetted by the thin layer of flowing nutrient. There are two basic problems with such tanks. First, gravity drains in these tanks may allow all nutrient solution to drain out quickly in the event of a power interruption or pump failure. This can result in the loss of an entire crop. Second, because these tanks are often rather long, the flow of nutrient can get restricted by heavy root growth. If plants are not monitored closely, the problem may not be found until significant damage has occurred.